In recent years, as one of causes of the global warming phenomenon, the greenhouse effect by CO2 has been pointed out, and countermeasures to protect the global environment have become urgent tasks internationally. CO2 generation sources include all human activity fields in which fossil fuels are burned, and there is a tendency for the demand for suppression of the discharge to be further strengthened. Accordingly, for power generation facilities such as thermal power plants that use large amounts of fossil fuels, methods of removing and recovering CO2 in combustion flue gas by bringing the combustion flue gas in industrial facilities such as a boiler or gas turbine into contact with an amine-based CO2 absorbent, and flue gas treatment systems for storing the recovered CO2 without release to the air have been studied vigorously.
As a process for removing and recovering CO2 from the combustion flue gas by using the above-mentioned amine-based CO2 absorbent, a CO2 recovery apparatus having a process for bringing combustion flue gas and the CO2 absorbent into contact with each other in a CO2 absorption tower (hereinafter, also simply referred to as “absorption tower”), and a process for heating the CO2 absorbent having absorbed CO2 in a CO2 absorbent regeneration tower (hereinafter, also simply referred to as “regeneration tower”) to cause CO2 to diffuse, regenerating the CO2 absorbent to be returned to the CO2 absorption tower for reuse is suggested (for example, refer to PTL 1).
In the CO2 absorption tower, CO2 in the flue gas is absorbed by the CO2 absorbent during countercurrent contact through a chemical reaction (exothermic reaction) by using the amine-based CO2 absorbent such as alkanolamines, and the flue gas from which CO2 has been removed is released to the outside of the system. The CO2 absorbent having absorbed CO2 is also called a rich solution. The rich solution is pressurized by a pump, is heated in a heat exchanger by a high-temperature CO2 absorbent (lean solution) which is regenerated by the diffuse of CO2 in the regeneration tower, and is supplied to the regeneration tower.
In the CO2 recovery process using the CO2 absorbent, CO2-removed flue gas from which CO2 has been removed from the combustion flue gas is released to the air. However, since an extremely small portion of a small amount of the amine absorbent is present in the released gas, it is necessary to reduce the amount thereof discharged.
Particularly in the future, when regulations on CO2 removal are started, there is a possibility that a CO2 removal facility itself may increase in size, and it is necessary to further reduce the amount thereof discharged.
As a technique for preventing the release of the amine absorbent, for example, a method in which a plurality of stages of washing units are provided on the downstream side of a CO2 absorption unit of a CO2 absorption tower of a CO2 removal apparatus to bring CO2-removed flue gas and washing water into gas-liquid contact with each other, thereby recovering an amine compound entrained in the CO2-removed flue gas (PTL 2) is suggested.
In addition, as another technique, a method in which sulfuric acid is sprayed from a sulfuric acid spraying device toward CO2-removed flue gas discharged from a CO2 absorption tower to cause an amine absorbent entrained in the discharged gas to become a basic amine compound sulfate, and a basic amine compound in gas discharged from a decarbonator that collects the basic amine compound sulfate is recovered, is suggested (PTL 3).
Furthermore, in the flue gas treatment system, there is a problem that in a case where mist generating substances which are generation sources of mist generated in an absorption tower in a CO2 recovery apparatus are contained in flue gas introduced into a CO2 absorption tower, that absorbs CO2, in the CO2 recovery apparatus, a CO2 absorbent contains the mist generating substances entrained therein, and thus the amount of the CO2 absorbent scattering toward the outside of the system increases. Therefore, countermeasures against this have been studied (PTL 4).